Clinoptilolite is not the most well known, but is one of the more useful natural zeolites.
Clinoptilolite is used in many applications such as a chemical sieve, a gas absorber, a feed additive, a food additive, an odor control agent and as a water filter for municipal and residential drinking water and aquariums.
Clinoptilolite is well suited for these applications due to its large amount of pore space, high resistance to extreme temperatures and chemically neutral basic structure.
What might strike many as odd is the food and feed additives.
Clinoptilolite has been used for several years now as an additive to feed for cows, pigs, horses and chickens.
It absorbs toxins in the feed that are created by molds and microscopic parasites and has enhance food absorption by these animals.
Similar uses in actual people food is being tested.
Clinoptilolite can easily absorb ammonia and other toxic gases from air and water and thus can be used in filters, both for health reasons and for odor removal.

Clinoptilolite forms as a devitrification product (the conversion of glass to crystalline material) of volcanic glass in tuffs.
Tuffs are consolidated pyroclastic rocks.
The devitrification occurs when the glass is in contact with saline waters.
Clinoptilolite is also found in the vesicles of volcanic rocks such as basalts, rhyolites and andesites.
It forms as an alteration of
phillipsite in deep-sea sediments and with
borate minerals in playa lakes.
Clinoptilolite, which means "oblique feather stone" in Greek, received its name because it was thought to be the monoclinic (or obliquely inclined) phase of the mineral ptilolite, as in "oblique ptilolite".
But ptilolite was later found to be the earlier named mineral
mordenite; consequently ptilolite is no longer in use.

Clinoptilolite is very closely related to
heulandite
and is currently being considered for disuse itself as it may just be a variety of huelandite.
It differs from heulandite significantly only in its enrichment in potassium and slightly more silica and it is argued that a separate mineral is not needed.
The name clinoptilolite is widely recognized and used among zeolite industries, mineral collectors and mineralogists.
For now at least, clinoptilolite is recognized as a legitimate, distinct mineral.

The structure of clinoptilolite is the same as heulandite and is sheet-like.
Although still a true tectosilicate where every oxygen is connected to either a silicon or an aluminum ion
(at a ratio of [Al + Si]/O = 1/2), there still is a sheet-like structural organization.
The sheets are connected to each other by a few bonds that are relatively widely separated from each other.
The sheets contain open rings of alternating eight and ten sides.
These rings stack together from sheet to sheet to form channels throughout the crystal structure.
The size of these channels controls the size of the molecules or ions that can pass through them and therefore a zeolite like clinoptilolite can act as a chemical sieve, allowing some ions to pass through while blocking others.
A zeolite can be thought of in terms of a house, where the structure of the house (the doors, windows, walls
and roof) is the zeolite while the furniture and people are the water and ammonia molecules and ions that can pass in and out of the structure.
Clinoptilolite's sheet-like structure produces the prominent pinacoid faces, the perfect cleavage and the unique luster on those faces.

PHYSICAL CHARACTERISTICS:

Color is colorless, white, pink, yellow, reddish and pale brown.

Luster is vitreous to pearly on the most prominent pinacoid face and on cleavage surfaces.

Transparency: Crystals are transparent to translucent.

Crystal System is monoclinic; 2/m

Crystal Habits include blocky or tabular crystals with good monoclinic crystal form.
More tabular and proportioned than heulandite.
Also commonly found in acicular (needle thin) crystal sprays.

Cleavage is perfect in one direction parallel to the prominent pinacoid face.

Fracture is uneven.

Hardness is 3.5 - 4, maybe softer on cleavage surfaces.

Specific Gravity is approximately 2.2 (very light)

Streak is white.

Other Characteristics: Can absorb a significant amount of water after drying and will retain its structure even if heated to almost the temperature of melted glass.